\subfloat[] {
\begin{tikzpicture}[scale=0.35]
	%% draw regular grid
	\draw[gray, very thin, step=0.25cm] (0,0) grid (8,8);
	
		% draw background ...
    \filldraw[fill=green, fill opacity=0.3] (0,0) rectangle +(8,8);
 
 		% draw first set of boxes ... red 
 		\foreach \x in {2,6}
 			\foreach \y in {2,6}
 				\filldraw[fill=red, fill opacity=0.3] (\x,\y) rectangle +(1,1);
 		
 		% draw first set of boxes ... red 
 		\foreach \x in {1,5}
 			\foreach \y in {0,4}
 				\filldraw	[fill=blue, fill opacity=0.3] (\x,\y) rectangle +(1,1);	
	%% The histogram ,,,
	%% red = 64, blue = 64, green 896, total = 1024
	\filldraw[fill=red, fill opacity=0.3] (0.5,-2) rectangle +(0.6,0.125);
	\filldraw[fill=blue, fill opacity=0.3] (1.5,-2) rectangle +(0.6,0.125);
	\filldraw[fill=green, fill opacity=0.3] (2.5,-2) rectangle +(0.6,1.75);
	
	\draw [->] (0,-2) -- (4,-2);
	\draw [->] (0,-2) -- (0,-0.2);
	
	\node at (6,-1) {$\textsc{H = 0.46}$};
\end{tikzpicture} 
}
\subfloat[] {
\begin{tikzpicture}[scale=0.35]

%% draw regular grid
\draw[gray, very thin, step=0.25cm] (0,0) grid (8,8);

% draw background ...
    \filldraw[fill=green, fill opacity=0.3] (0,0) rectangle +(8,8);
 
 		% draw first set of boxes ... red 
 		\filldraw[fill=red, fill opacity=0.3] (2.25,2.75) rectangle +(1,1);
 		\filldraw[fill=red, fill opacity=0.3] (2.75,6.25) rectangle +(1,1);
 		\filldraw[fill=red, fill opacity=0.3] (5.75,2.5) rectangle +(1,1);
 		\filldraw[fill=red, fill opacity=0.3] (6.25,6.75) rectangle +(1,1);
 		
 		
 		% draw first set of boxes ... red 
 		\filldraw	[fill=blue, fill opacity=0.3] (1.75,1.5) rectangle +(1,1);
 		\filldraw	[fill=blue, fill opacity=0.3] (1.5,4.25) rectangle +(1,1);
 		\filldraw	[fill=blue, fill opacity=0.3] (4.25,0.75) rectangle +(1,1);
 		\filldraw	[fill=blue, fill opacity=0.3] (4.25,4.5) rectangle +(1,1);
 		
 		%% The histogram ,,,
	%% red = 64, blue = 64, green 896, total = 1024
	\filldraw[fill=red, fill opacity=0.3] (0.5,-2) rectangle +(0.6,0.125);
	\filldraw[fill=blue, fill opacity=0.3] (1.5,-2) rectangle +(0.6,0.125);
	\filldraw[fill=green, fill opacity=0.3] (2.5,-2) rectangle +(0.6,1.75);
	
	\draw [->] (0,-2) -- (4,-2);
	\draw [->] (0,-2) -- (0,-0.2);
	
	\node at (6,-1) {$\textsc{H = 0.46}$};
\end{tikzpicture}
}
\subfloat[] {
\begin{tikzpicture}[scale=0.35]

%% Now Draw the octree ...
  \draw [help lines]
  		 [step = 2cm]       (0,0) grid (8,8);
  
  \foreach \x in {2,6}
  	\foreach \y in {2,6}
  		\draw [help lines, step=1cm] (\x,\y) grid +(2,2);
  
  \foreach \x in {0,4}
  	\foreach \y in {0,4}
  		\draw [help lines, step=1cm] (\x,\y) grid +(2,2);
  		  
    % The scene   
 		% draw background ...
    \filldraw[fill=green, fill opacity=0.3] (0,0) rectangle +(8,8);
 
 		% draw first set of boxes ... red 
 		\foreach \x in {2,6}
 			\foreach \y in {2,6}
 				\filldraw[fill=red, fill opacity=0.3] (\x,\y) rectangle +(1,1);
 		
 		% draw first set of boxes ... red 
 		\foreach \x in {1,5}
 			\foreach \y in {0,4}
 				\filldraw	[fill=blue, fill opacity=0.3] (\x,\y) rectangle +(1,1);

	%% The histogram ,,,
	%% red = 4, blue = 4, green = 32, total = 40
	\filldraw[fill=red, fill opacity=0.3] (0.5,-2) rectangle +(0.6,0.2);
	\filldraw[fill=blue, fill opacity=0.3] (1.5,-2) rectangle +(0.6,0.2);
	\filldraw[fill=green, fill opacity=0.3] (2.5,-2) rectangle +(0.6,1.6);
	
	\draw [->] (0,-2) -- (4,-2);
	\draw [->] (0,-2) -- (0,-0.2);
	
	\node at (6,-1) {$\textsc{H = 0.64}$};
\end{tikzpicture} 
}
\subfloat[] {
\begin{tikzpicture}[scale=0.35]

%% Now Draw the octree ...
	
  \draw [help lines]
 			 [step = 2cm]       (0,0) grid (8,8)
 			 [step = 1cm]       (0,0) grid (6,6)
 			 [step = 1cm] 			(6,2) grid +(2,2)
 			 ;
   
   \draw [help lines] 
   				[step=0.5cm] (4,0) grid +(2,2)
   				[step=0.5cm] (4,4) grid +(2,2)
   				[step=0.5cm] (1,4) grid +(2,2)
   				[step=0.5cm] (5,2) grid +(2,2)
   				[step=0.5cm] (2,2) grid +(2,2)
   				[step=0.25cm] (4,0.5) grid +(1.5,1.5)
   				[step=0.5cm] (1,1) grid +(2,2)
   				[step = 0.5cm] 			(2,6) grid +(2,2)
 			 		[step = 0.5cm] 			(6,6) grid +(2,2)
 			 		[step=0.25cm] (2.5,6) grid +(1.5,1.5)
 			 		[step=0.25cm] (6,6.5) grid +(1.5,1.5)		
 			 		
 			 		[step=0.25cm] (1.5,1.5) grid +(0.5,1.0)
 			 		[step=0.25cm] (2.5,1.5) grid +(0.5,1.0)		
 			 		[step=0.25cm] (2,2.5) grid +(1.5,0.5)
 			 		[step=0.25cm] (2,3.5) grid +(1.5,0.5)
 			 		[step=0.25cm] (2,3) grid +(0.5,0.5)
 			 		[step=0.25cm] (3,3) grid +(0.5,0.5)
 			 		
 			 		[step=0.25cm] (5.5, 2.5) grid +(0.5,1.0)
 			 		[step=0.25cm] (6.5, 2.5) grid +(0.5,1.0)
 			 		[step=0.25cm] (4, 4.5) grid +(0.5,1.0)
 			 		[step=0.25cm] (5, 4.5) grid +(0.5,1.0)
 			 		[step=0.25cm] (1.5, 4) grid +(1.0,0.5)
 			 		[step=0.25cm] (1.5, 5) grid +(1.0,0.5)
   				;		 
   		 
%% The scene	
% draw background ...
    \filldraw[fill=green, fill opacity=0.3] (0,0) rectangle +(8,8);
 
 		% draw first set of boxes ... red 
 		\filldraw[fill=red, fill opacity=0.3] (2.25,2.75) rectangle +(1,1);
 		\filldraw[fill=red, fill opacity=0.3] (2.75,6.25) rectangle +(1,1);
 		\filldraw[fill=red, fill opacity=0.3] (5.75,2.5) rectangle +(1,1);
 		\filldraw[fill=red, fill opacity=0.3] (6.25,6.75) rectangle +(1,1);
 		
 		
 		% draw first set of boxes ... red 
 		\filldraw	[fill=blue, fill opacity=0.3] (1.75,1.5) rectangle +(1,1);
 		\filldraw	[fill=blue, fill opacity=0.3] (1.5,4.25) rectangle +(1,1);
 		\filldraw	[fill=blue, fill opacity=0.3] (4.25,0.75) rectangle +(1,1);
 		\filldraw	[fill=blue, fill opacity=0.3] (4.25,4.5) rectangle +(1,1);
 		
 	%% The histogram ,,,
	%% red = 55, blue = 46, green = 197, total = 298
	\filldraw[fill=red, fill opacity=0.3] (0.5,-2) rectangle +(0.6,0.37);
	\filldraw[fill=blue, fill opacity=0.3] (1.5,-2) rectangle +(0.6,0.31);
	\filldraw[fill=green, fill opacity=0.3] (2.5,-2) rectangle +(0.6,1.32);
	
	\draw [->] (0,-2) -- (4,-2);
	\draw [->] (0,-2) -- (0,-0.2);
	
	\node at (6,-1) {$\textsc{H = 0.87}$};
\end{tikzpicture}
}